The Brookings Institution estimated it would cost $12 billion a year in teacher salaries alone to decrease class sizes nationally by one student. And that was in 2011, when class sizes were smaller and teacher salaries lower than they are now.

That’s a lot of cash. Cash that could probably do more for schools if it were invested elsewhere.

How big are Arizona classes?

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Arizona has the nation's largest student-to-teacher ratio. What might it cost to meaningfully lower it?
Joanna Allhands, opinion columnist

It’s hard to know exactly how big Arizona classes have become. The state does not require schools to report their real-life class sizes, which can vary widely by grade and district. So, the best estimates we’ve got involve broad student-to-teacher ratios, which are determined by dividing a state’s total number of students by its total number of teachers.

According to the National Center for Education Statistics, there were 23 students per Arizona teacher in 2016-17 – the nation’s highest. The national average, by comparison, was 16 students.

Arizona’s ratio has increased steadily since 2011, even as other states have held class sizes steady or decreased them.

But that doesn’t mean the average Arizona classroom contains 23 students. One study suggests student-to-teacher ratios can underestimate real-life class sizes by as many as 10 students.

Should smaller classes be a priority?

Some of the larger, more reliable studies suggest that significantly lowering class sizes – by seven to 10 students per class – can have lasting benefits for students, particularly if those efforts are focused in kindergarten through third grade or in schools with significant socioeconomic challenges. But the extent of those benefits can vary widely, depending on the grade and school.

That doesn’t mean class sizes don’t matter. They do. Common sense tells us a 40-kid elementary class is untenable, even if we’re not sure how common such classes are in Arizona.

But even if we identified the schools with the largest classes and targeted investments to K-3 and high-poverty schools – and it may make sense to do so – it would still likely require hundreds of millions of dollars to lower class sizes enough to make a measurable impact.

And that’s assuming we can find enough teachers to fill the extra classroom slots.

Some researchers suggest it might be smarter to focus on improving teacher quality, because having a highly effective teacher in the classroom affects the quality of education more than anything else.

If quality matters, how do we get it?

But what do we mean by teacher quality? This is where it gets thorny.

That’s because for all the research we’ve done (and there are studies galore that back a wide range of conclusions), we still can’t agree on what makes a teacher most effective – much less how to fairly measure it.

Some argue that effective teachers can be identified by how much they grow their students' skills. Others maintain that effective instruction hinges on factors like how well teachers check for comprehension and adjust their lessons if students didn’t get the concept.

Still others say it’s the intangibles that make the most effective teachers, such as how well they know their students’ needs, how well they can engage them in lessons and how much they inspire them to excel.

States have spent a lot of time arguing about the metrics to measure these broad concepts, and most still are getting it wrong. Largely, because these systems aren’t set up to ferret out individual areas of improvement.

Why the metrics don't always match

The lion's share of the evaluation work falls on overburdened principals, who spend hours in classrooms but often struggle to fully document what teachers are doing well and where (and how) they can grow their skills.

So, though most principals can identify teachers that are struggling or need support, most evaluations produce Lake Wobegon teachers: Almost all are rated above average.

Will schools seize this opportunity?

Teachers crave collaboration with their peers. They want to learn from each other and get feedback as they are delivering lessons, not weeks after the fact in an after-school training session.

Schools should focus resources on offering this support during the school day and for all teachers, not just those that are new to the profession. And once they have it in place, they should consider using it as a foundation for their evaluation systems.

If the goal is to continually grow teachers' skills, why wouldn't we leverage the help of master teachers to provide more positive, ongoing feedback? It would be far more effective than relying on a single standardized test score and a few formal visits from the principal.

Schools have been given a golden opportunity here to think critically about what they value most from their teachers and how to foster it.